// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_
#define UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_

#include "ui/aura/aura_export.h"

namespace aura {
class Window;

namespace client {

    class AURA_EXPORT ActivationChangeObserver {
    public:
        // The reason or cause of a window activation change.
        enum class ActivationReason {
            // When a window is activated due to a call to the ActivationClient API.
            ACTIVATION_CLIENT,
            // When a user clicks or taps a window in the 2-dimensional screen space.
            INPUT_EVENT,
            // When a new window is activated as a side effect of a window
            // disposition changing.
            WINDOW_DISPOSITION_CHANGED,
        };

        // Called when |gained_active| gains focus, or there is no active window
        // (|gained_active| is NULL in this case.) |lost_active| refers to the
        // previous active window or NULL if there was no previously active
        // window. |reason| specifies the cause of the activation change.
        virtual void OnWindowActivated(ActivationReason reason,
            Window* gained_active,
            Window* lost_active)
            = 0;

        // Called when during window activation the currently active window is
        // selected for activation. This can happen when a window requested for
        // activation cannot be activated because a system modal window is active.
        virtual void OnAttemptToReactivateWindow(aura::Window* request_active,
            aura::Window* actual_active) { }

    protected:
        virtual ~ActivationChangeObserver() { }
    };

    // Gets/Sets the ActivationChangeObserver for a specific window. This observer
    // is notified after the ActivationClient notifies all registered observers.
    AURA_EXPORT void SetActivationChangeObserver(
        Window* window,
        ActivationChangeObserver* observer);
    AURA_EXPORT ActivationChangeObserver* GetActivationChangeObserver(
        Window* window);

} // namespace client
} // namespace aura

#endif // UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_
